1. Field of the Invention
This invention relates to a process for the nitration of aromatic hydrocarbons. More particularly, this invention relates to a process for the vapor phase nitration of aromatic hydrocarbons selected from the group consisting of benzene and toluene in the presence of a molecular sieve catalyst.
Nitrated aromatic hydrocarbons find use as solvents, explosives, dyes, perfumes, and analytical reagents, and are important as intermediates in organic synthesis. As an example, nitrated aromatic hydrocarbons are convertible by reduction into primary amines, which, in turn, are valuable intermediates in the synthesis of dyes, pharmaceuticals, photographic developers, antioxidants, and gum inhibitors.
2. Description of the Prior Art
Vapor phase nitration of aromatic hydrocarbons is known in the art. The vapor phase nitration of benzene and toluene at temperatures ranging from about 275.degree. C. to about 310.degree. C. is described in McKee and Wilhelm, Industrial and Engineering Chemistry, 28(6), 662-667 (1936) and U.S. Pat. No. 2,109,873. McKee and Wilhelm catalyzed their reaction with silica gel, with best results being reported by the use of 14 mesh material. Bauxite and alumina were reported to be ineffective as catalysts in the vapor phase nitration of benzene. U.S. Pat. No. 2,431,585 describes a vapor phase nitration of aromatic hydrocarbons at temperatures from 130.degree. C. to 430.degree. C. in the presence of a catalyst selected from the group consisting of metal metaphosphates, boron phosphate, and solid and supported phosphoric acid catalysts. Preferred catalysts are the metal metaphosphates such as those of calcium, iron, and magnesium. More recently, U.S. Pat. No. 4,112,006 described a process for nitrating toluene in the vapor phase in the presence of an acidic inorganic catalyst consisting of a carrier substance based on silica and/or alumina impregnated with a high boiling inorganic acid such as sulfuric acid or phosphoric acid and, optionally, with metal salts of such acids. The reaction is run under reduced pressure at temperatures from about 80.degree.-180.degree. C., with 100.degree. C. to 140.degree. C. being preferred.
The use of molecular sieve catalysts having a pore size varying from about 5 .ANG. to about 10 .ANG. is described in U.S. Pat. No. 4,107,220 as an effective catalyst for controlling the para/ortho isomer distribution of nitrochlorobenzene during the vapor phase nitration of chlorobenzene. A suitable temperature range was reported to be from about 190.degree. C. to about 290.degree. C.
Although these prior art processes for the vapor phase nitration of aromatic hydrocarbons generally provide the desired product, they nevertheless are limited in their applications. Principal among these limitations are low (aromatic hydrocarbon) conversions and contamination of the nitrated aromatic hydrocarbon product by undesirable by-products and the complicated nature of the catalysts.